Small Engines (Lawn Mowers, etc.): Honda 16.5 HP engine surges, speed nozzle, hp engine

Question
I have a Sears lawn tractor with Honda 16.5 HP v-twin engine(model #GXV 530-EXA1) It just recently started to "surge" when not under a load.  It happens at full speed down to medium slow speed.  At idle the engine will stop.  The right plug is nice and clean, the left plug has carbon on it. It also "backfires" slightly at meduium-fast to meduium slow speeds.I have always used STA-BIL in the fuel.

Answer
It appears you have a fuel system restriction or very old poor fuel.. It sounds like your high speed nozzle may be plugged or you have dirt in the carb.  I would start by doing a good carb cleaning.  If this doesnt resolve it send me a followup and i will help you troubleshoot more.Is your fuel fresh?  By fresh I mean within 10 days from the pump.